This invention relates to a method and an apparatus for creating pseudo-herringbone-type gears from ordinary helical gears, and to gears produced thereby, particularly in matched pairs.
In comparing common types of power transmission gears, a helical gear which has angled teeth, typically has a higher load carrying capacity than the common spur gear, which has straight-cut teeth, of the same size. Also, because the helical gear runs more smoothly than the correspondingly spur gear, helical gears can normally operate at much higher speeds than can spur gears. However, in operation helical gears also create an axial thrust which may have to be absorbed by the bearings if same are employed to carry the gear. Relatively expensive bearings such as thrust bearings are normally employed to absorb such axial forces.
The advantages of a helical gear can be obtained, without the requirement of thrust bearings, however, through use of a herringbone gear. A herringbone gear is constructed of two adjacent rows of helical or angled gear teeth which extend around the circumference of the gear with the two rows of teeth being oppositely angled. By providing the two rows of oppositely angled gear teeth, axial forces normally created by a helical gear, are avoided. Any axial thrust created by one row of angled teeth is cancelled by the opposite acting reaction axial thrust created by the other row of angled teeth. Overall, herringbone gears possess advantages over other gear types in that (1) there is a continuous smooth meshing of gear teeth; (2) they afford greater strength; (3) there is the absence of end or axial thrust as noted above; (4) they may be operated at high peripheral speeds; and (5) they possess the the ability to withstand shock loads and loads of a vibrating nature because of very low backlash.
Herringbone gears, however, are difficult and costly to manufacture, requiring complex machine tools for manufacture. Consequently, the cost of herringbone gears is quite high. Additionally, conventional herringbone gears cannot be fully heat treated due to a lack of any equipment for finishing same after a heat treatment step. In fact, though herringbone gears are often preferred for certain mechanical environs, the cost for same has historically been prohibitive, and lesser desirable substitute gears have been employed in lieu of same.
An alternative approach to the true herringbone gear is a pseudo herringbone gear. Pseudo herringbone gears are generally known in the prior art, and conventionally include a two oppositely angled helical gears coupled together to form a composite gear. Such pseudo herringbone gears are, for example, disclosed in U.S. Pats. Nos. 4,429,586; 1,070,589; 1,320,459; 1,394,080; 1,464,108; 1,551,844; 3,545,296; 3,686,968; 3,307,433; 3,486,394; 2,982,144; 2,703,021; 3,160,026; 3,102,433; 2,734,396 and 4,022,083. Methods disclosed in the above listed patents for production of pseudo herringbone gears are relatively complicated and do not generally allow for use of off-the-shelf gears.
The present invention is directed to pseudo herringbone gears and affords the possibility of use of conventional off-the-shelf helical gears for the production of pseudo herringbone gears, particularly in matched pairs. Neither the apparatus nor the method of the present invention for producing pseudo herringbone gears, nor the particular gears per se is taught or suggested by the above listed patents, nor any other known prior art.